A fine pigment has a tendency to be strong in the aggregation force between the pigment particles in a medium such as an organic solvent or a molten resin. Accordingly, in a color developed matter, a fine pigment sometimes causes color unevenness or remarkable degradation of pigmenting power. Further, a fine pigment causes a problem such as the degradation of the gloss with respect to the colored surface or the coating film of the color developed matter.
As a method for improving the dispersibility of a pigment, there has hitherto been used a polymer dispersant which has a moiety having the affinity to the pigment and a polymer moiety imparting the dispersibility in the medium. For example, PTL 1 discloses a polymer pigment dispersant for use in a toner, wherein in the polymer pigment dispersant an azo or a diazo chromophore containing a substitution product of an acetoacetanilide is bonded to the polymer. Also, PTL 2 discloses an example of the use of a comb-type polymer dispersant having an acid or basic moiety known as Solsperse (registered trademark). On the other hand, PTL 3 discloses an example of the use of a polymer dispersant as a dispersant for an ink-jet recording pigment, wherein the polymer dispersant is obtained by bonding to the water-soluble polymer main chain a chromophore having a molecular weight smaller than 95% of the molecular weight of an azo pigment.